G3VPX HF Transceiver - brief specification

 

IFs

    45.000 Mhz     Filter - MOSFET - Filter   (4 pole 20kHz wide crystal filters from Surplus Sales of Nabraska)

    8.215 MHz     Yaesu filters - 2.0kHz and 500Hz receive, 2.4kHz transmit (Thanks eBay!!)

    455 kHz       Yaesu 2kHz filter on transmit and Murata 2.4kHx (ex FT847) filter on receive

 

Oscillators

   1st LO - AD9854ASQ DDS - (with heatsinking!!) , 47 - 75 Mhz.

       Clock: 200Mhz Pletronics low phase noise osc.

       Output filtering: five switched BPFs and 76Mhz Cauer LPF

   2nd LO - 47.215 Mhz crystal osc

    3rd LO - 8.67MHz crystal osc

    CIO - AD9854 DDS - 453.750 etc   106Mhz DDS clock. Murata 20kHz wideoutput filter

Using DDS chip for CIO allows IF shift (using PIC chip ADC input) and key pad adjustment of CIO whilst transmitting.

 

Mixers

   1st and 2nd are bidirectional (PIN diode swichted) ADE-1 ring diode mixer.

   3rd mixers Rx 8.215Mhz-455kHz and Tx 455kHz-8.215Mhz are AD831 balanced mixer chips

   Tx balanced modulator and Rx demodulator are AD831 balanced mixer chips.

 

RF filters - 4 pole Chebychev filter for each band. Designed using free ELSIE software, aligned on HP 3585A spectrum analyser, PIN diode switched.

 

RF preamp - relay switched MAX2111 50ohm 18dB amp chip

 

Microprocessor

PIC18F452 running at 32Mhz (8 MHz ext clock + 4x PLL quadrupling).

Programmed using PIC Basic - in-situ programmed

(Use of PIC Basic allowed upgrade from PIC16F877 to pin compatible PIC18F452 without any reprogramming

    - despite different assembly language and asssembler program ... which was located and used automatically.)

PIC board - multiplexing/ demultiplexing of inputs / outputs, rotary encoder 8 bit counter, DDS 5/3.3 level change resistors.

Band, CIO, filter, band power switching all routed through PIC board

Key pad for digital frequency entry, A/B VFO switching and set-up functions (eg band -power and Tx CIO offset)

Tuning using an Agilent 256 pulse/rev rotary encoder (10, 50 and 100Hz steps)

PIC chip remembers last frequency used on each band and has programed band limits.

Set up functions programmed so far:

F1 - Set Tx 45Mhz gain - stored for current band

F2 - set RF drive attenuator (0 2 4 6 8 10 12 14 dB) - stored per band.

F3 - Tx LSB offset from filter centre (0 - 2000, using 1350) - Can alter with main tuning dial whist transmitting (first local osc automatically shifted to compensate for shift)

F4 - Tx USB offset from filter centre ( as F3)

F5 - Transceiver frequency calibration. eg: 3.7Mhz signal generator, Set dial to read 3.7Mhz. Then F4 and rotate tuning dial to zero beat.

F9 - switch DSP into RX signal patch. ... changes CIO to generate 15 kHz 4th IF rather then audio and feeds this to DSP board. Dsp output to Rx audio.

 

Only used 13.5kByte of pragram memory. 32kbyte available.

 

ALC board - RF drive, SWR FWD/REV metering + protection. Digitally set power levels per band.

 

Power amplifier

20 watt kit built unit from project 12 years ago

120watt bipolar PA - not yet working 'cleanly' !!

Six relay switched LP filters.

 

Construction: Three layer case, PA slot at back, front panel offset from chassis to give freedom of layout. MDF/hardwood front panel 15mm in front of internal Aluminium front panel.

 

DSP - Texas instruments TMS320VC5416 DSK development board and programming suite. This board now installed and can be be switched into receive path via keypad.

When switched in, CIO frequency is 440kHz or 470kHz to generate 15kHz 4th IF. Demodulation etc then to be done in DSP. Still need to program my brain in how to program this board!

CIO output filter had to changed from 8kHz wide to 35kHz wide to occomadate 440kHz and 470kHz.